By H. G. Davies, Ralph Green, D. R. Kelly and Stanley M. Roberts (Auth.)
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Extra info for Biotransformations in Preparative Organic Chemistry. The Use of Isolated Enzymes and Whole Cell Systems in Synthesis
However, the catalytic activity is not restricted solely to amide hydrolysis; a wide range of ester and related functions is susceptible to hydrolysis with a-chymotrypsin [3,4]. A well-defined model for the active site of α-chymotrypsin has been proposed  in which the site is considered to consist of four pockets, each one of which uniquely corresponds to each of the four groups attached to the α-carbon atom of a specific substrate. It was recognized [2,6] many years ago that α-chymotrypsin exhibits L stereospecificity towards its amino acid substrates.
However, the rate of hydrolysis with α-chymotrypsin, bakers' yeast and Rhizopus was so slow that it militated against their use in organic synthesis. In addition the chemical yield obtained was much higher for the acetate (110) than the propionate (111) and the butanoate (112). Thus, the acetate (110) was hydrolysed in the presence of PLE to give (-)-(15,4Λ) alcohol (113) in 86% yield with 86% enantiomeric excess, whereas the lipase from Candida cylindracea afforded the ( + )-(IR,4S) alcohol (114) in 82% yield.
Incubation of the diester (27) with PLE at pH 8 for 1 h gave the monoester (28) in 85% yield. This material was converted into the lactone (57) which was obtained in 64% enantiomeric excess. 1. CARBOXYLIC ACID ESTER BONDS 39 preferentially cleaved the pro-(5) ester group of the compound (27), thus displaying the same catalytic profile as α-chymotrypsin for this reaction. The same diester (27) was also subjected to incubation with various microorganisms and, although most of these preferentially attacked the pro-(R) ester group, the monoesters were obtained in varying degrees of optical purity.
Biotransformations in Preparative Organic Chemistry. The Use of Isolated Enzymes and Whole Cell Systems in Synthesis by H. G. Davies, Ralph Green, D. R. Kelly and Stanley M. Roberts (Auth.)